Athens is one of Europe's better-value capitals. Budget travelers can manage €40-60/day: guesthouses near the Acropolis run €25-40, a souvlaki lunch costs €3-4, a sit-down mezedes dinner with wine €15-20 per person. The Acropolis combined ticket (€30) covers 7 sites and is valid for 5 days.
Mid-range travelers (€80-120/day) can stay in comfortable boutique hotels in Plaka or Monastiraki, eat at excellent restaurants, and do day trips by bus. Athens is a walkable city — a taxi from anywhere in the center costs €5-10 maximum. Sunday is free admission day at state museums outside peak season.